David Smith, Michael LeHew, and Joe Groff, explaining why they chose backslash (\) as the syntax for their new key path proposal for Swift:

During review many different sigils were considered:

No Sigil: This matches function type references, but suffers
from ambiguity with wanting to actually call a type property.
Having to type let foo: KeyPath<Baz, Bar> while consistent with
function type references, really is not that great (even for
function type references).

Backtick: Borrowing from Lisp, backtick was what we used in
initial discussions of this proposal (it was easy to write on a
white-board), but it was not chosen because it is hard to type in
Markdown, and comes dangerously close to conflicting with other
parser intrinsics.

In short, to include a literal backtick inside a <code> span, you can just use two backticks as the opening and closing delimiters. This input:

```Person.friends[0].name``

produces this HTML output:

<code>`Person.friends[0].name</code>

For the sake of clarity, you can include a space at the beginning (or end) of the delimited code span, which will be omitted from the output, like this:

`` `Person.friends[0].name``

Far be it for me to tell the Swift folks what to do, but I think backtick looks far better in the above example than backslash does. To me, backslash in any language should mean “escape the following character” and nothing else.